Paper products are used for a variety of purposes. Paper towels, facial tissues, toilet tissues, and the like are in constant use in modern industrialized societies. The large demand for such paper products has created a demand for improved versions of the products. If the paper products such as paper towels, facial tissues, toilet tissues, and the like are to perform their intended tasks and to find wide acceptance, they must possess certain physical characteristics. Among the more important of these characteristics are strength, softness, and absorbency.
Strength is the ability of a paper web to retain its physical integrity during use.
Softness is the pleasing tactile sensation consumers perceive when they use the paper for its intended purposes.
Absorbency is the characteristic of the paper that allows the paper to take up and retain fluids, particularly water and aqueous solutions and suspensions. Important not only is the absolute quantity of fluid a given amount of paper will hold, but also the rate at which the paper will absorb the fluid.
U.S. Pat. No. 3,537,954 issued to Justus discloses a web formed between an upper fabric and a lower forming wire. A pattern is imparted to the web at a nip where the web is sandwiched between the fabric and a relatively soft and resilient papermaking felt. U.S. Pat. No. 4,309,246 issued to Hulit et al. discloses delivering an uncompacted wet web to an open mesh imprinting fabric formed of woven elements, and pressing the web between a papermaker's felt and the imprinting fabric in a first press nip. The web is then carried by the imprinting fabric from the first press nip to a second press nip at a drying drum. U.S. Pat. No. 4,144,124 issued to Turunen et al. discloses a paper machine having a twin-wire former having a pair of endless fabrics, which can be felts. One of the endless fabrics carries a paper web to a press section. The press section can include the endless fabric which carries the paper web to the press section, an additional endless fabric which can be a felt, and a wire for patterning the web.
PCT Publication WO95/17548 having a U.S. priority date of Dec. 20, 1993 and published Jun. 29, 1995 in the name of Ampulski et al.; and PCT Publication WO96/00813 having a U.S. priority date of Jun. 29, 1994 and published Jan. 11, 1996 in the name of Trokhan et al. disclose papermaking methods employing dewatering felt layers.
While suitable methods of making paper webs are disclosed in the art, paper scientists continue to search for even better methods of making patterned paper structures economically and with increased strength, without sacrificing softness and absorbency.
Through-air dried paper webs are made as described in U.S. Pat. No. 4,514,345 issued to Johnson et al on Apr. 30, 1985; U.S. Pat. No. 4,528,239 issued to Trokhan on Jul. 9, 1985; and U.S. Pat. No. 5,334,289 issued to Trokhan et al on Aug. 2, 1994, all three patents are assigned to The Procter and Gamble Company and incorporated herein by reference. Paper produced by through air drying is disclosed in U.S. Pat. No. 4,529,480 and U.S. Pat. No. 4,637,859, both issued in the name of Trokhan, which patents are incorporated herein by reference. The paper of these patents is characterized by having two physically distinct regions: a continuous network region having a relatively high density and a region comprised of a plurality of domes dispersed throughout the whole of the network region. The domes are of relatively low density and relatively low intrinsic strength compared to the network region.
Generally, through-air drying papermaking processes include several steps. An aqueous dispersion of the papermaking fibers is formed into an embryonic web on a foraminous member, such as a Fourdrinier wire. This embryonic web is associated with a deflection member having a macroscopically monoplanar, continuous, patterned non-random network surface which defines within the deflection member a plurality of discrete, isolated deflection conduits. The papermaking fibers in the embryonic web are deflected into the deflection conduits and water is removed through the deflection conduits to form an intermediate web. The intermediate web may optionally be dried and foreshortened by creping. Creping is a process of the removal of the dried intermediate web from the surface (usually, also drying surface, such as the surface of a Yankee dryer) with a doctor blade to form a finished paper web.
Deflection of the fibers into the deflection conduits can be induced by, for example, the application of differential fluid pressure to the embryonic paper web. One preferred method of applying differential pressure is by exposing the embryonic web to a vacuum through the deflection conduits. As a result of a sudden application of the vacuum pressure, a deflection of the fibers into the deflection conduits occurs, which can lead to separation of the deflected fibers from each other and from the embryonic web. In addition, as a result of a sudden application of a vacuum pressure, a certain number of partially dewatered fibers separated from the embryonic web could completely pass through the papermaking belt. These phenomena cause formation of pin-sized holes, or pinholes, in the domes of the finished paper web and clogging the vacuum dewatering machinery.
The undesirable creation of pinholes in the domes of the paper web, or pinholing, was mitigated by commonly assigned U.S. Pat. No. 5,334,289, issued on Aug. 2, 1994 to Trokhan et al. and incorporated by reference herein. This patent provided surface texture irregularities in the backside network. The backside irregularities mitigate the effect of a sudden application of a vacuum pressure. Still, the search for improved products has continued.
Accordingly, it is an object of the present invention to provide a papermaking process which substantially reduces the pinholing in the finished paper web and the buildup of paper fibers on the vacuum dewatering machinery.
It is another object of the present invention to provide a papermaking process which allows to produce a paper sheet that has a more uniform basis weight distribution and a more uniform density distribution, relative to the papers produced by the through-air drying processes of the prior art.
It is further object of the present invention to provide a novel method for dewatering and molding a paper web.
It is still another object of the present invention to provide a method of enhancing water removal from a web during pressing of the web.